1. Field of the Invention
This invention relates generally to producing a media master, and more particularly to writing curvilinear servo sector patterns on a media master.
2. Background Art
Many data storage disk systems incorporate an actuator arm that carries a read/write head above the surface of a disk. The actuator arm is coupled to an actuator assembly that causes the arm to rotate about a pivot point. This causes the head to travel along an arc segment corresponding to a circle centered about the pivot point with a radius determined by the length of the actuator arm.
During operation, the rotation of the disk and the movement of the head provide a location of the head relative to the disk surface. A typical disk includes many servo sectors which collectively form a servo sector pattern. The servo sector pattern provides encoded information that is read during disk operations to determine the location of the head relative to the disk surface.
One type of servo sector pattern is radially aligned. The servo sectors are aligned with a disk radius and extend between the inner diameter and the outer diameter of the disk. The servo sectors divide the usable data zone into a corresponding plurality of data wedges, and the disk surface includes a plurality of concentric data tracks which are typically spaced at a constant pitch T.sub.p.
A problem with the radially aligned servo sectors is that they are not aligned with the arc segment along which the head typically travels. It is more desirable to have servo sectors that are aligned with the arc segment, so that a head traveling over a disk rotating at constant speed will encounter servo sectors at a constant rate, independent from the radial position of the head. Although they are shaped differently, the spacing, number and encoded information in the arc segment shaped servo sectors can be the same as their radially aligned counterparts.
One mechanism for producing disks is from a master disk having the desired servo sector pattern. A conventional master writing tool can comprise an air bearing spindle onto which a glass master substrate is mounted. To write the master, the glass substrate is uniformly coated with photoresist which is exposed by an optical spot. A linear actuator whose position is sensed by a laser inteferometer can be used to radially position the spot. In conventional fashion, the exposed spots are used to produce pits on the master disk. The master disk provides a mold that, using conventional techniques, is used to make data storage disks.
A conventional master writing system can generate an index pulse corresponding to each disk revolution and include a precision angle encoder for determining the circumferential positioning of the master disk. This information and a bit map of the servo sector data can be used to write a master having a radially aligned servo sector pattern. Conventional master writing systems are inadequate for producing arc segment shaped servo sector patterns for various reasons. For one, the conventional system uses a coordinate system that assumes a radially aligned servo sector. Additionally, increased resolution is needed to ensure that adjacent pit locations are evenly aligned along the arc segment shape. This requires much more memory and presents a throughput problem.
Thus, there remains a need for a master writing system that can produce curvilinear (e.g. arc segment) shaped servo sector patterns.
SUMMARY OF THE INVENTION
The present invention provides apparatuses and methods for producing curvilinear servo sector patterns, as well for generating master writer control settings that are used to produce curvilinear servo sector patterns.
In certain embodiments, offsets between a radially aligned reference and the desired curvilinear servo sector are determined, and these offsets are used to produce the curvilinear servo sector pattern using information (such as a bit map) that is ordinarily used to produce a radially aligned servo sector pattern.
The offset between the radially aligned reference and the curvilinear servo sector pattern is a function of the radial position on the surface of the disk. This radial position can be determined according to the track number. Thus, a plurality of offsets can be determined, with each offset associated with one or more tracks. Each offset can be converted into a delay which is the amount of time that it takes for the disk to rotate through the offset, or from the radially aligned reference axis to the curvilinear servo sector.
The delay can be converted into master writer control settings that are used to produce the curvilinear servo sector pattern. For example, the delay can be converted into sector delay, clock cycle delay and residual delay values. The sector, clock cycle and residual delay values each represent a portion of the delay. The sector delay is an integer number of sectors that the offset spans (i.e. the number of intervening servo sectors). This number of sectors may not account for the full delay. The remaining delay is provided by the clock cycle delay, which is an integer number of clock cycles, and a residual delay, which is a fractional clock cycle.
The sector, clock cycle and residual delay values can be converted into bytes of data used to control a master writer. The master writer can implement the same mapping information for the encoded information in a radially aligned servo sector pattern to produce the curvilinear servo sector pattern because the control settings cause the master writer to delay the generation of laser pulses by an amount that corresponds to the offset between the radially aligned case and the curvilinear case.
In other embodiments, a piece-wise linear approximation of the curvilinear shape can be implemented to reduce the amount of required control data. In one embodiment, this is done by determining an interpolation constant for each linear piece, and adjusting the delay values accordingly. In lieu of a series of values, the residual delay portion can thus have a base value and a linear increment.
In still further embodiments, a master writer controller that generates pulses for multiple lasers can also be implemented. The first and second laser pulse streams can have different pulse parameters and different offsets. To accommodate these differences, the master writer control circuitry that defines the pulse parameters and provides the residual delay (fractional clock cycles) can be replicated.